Microtubule-severing plays important roles in development, including for cell structure and division. Katanin, encoded by
mei-1 and
mei-2, is a microtubule-severing complex required for the assembly of the meiotic spindle and then must be downregulated in the span of 20 minutes, to allow for formation of the mitotic spindle. Cullin-based ubiquitin ligases (CUL-2, CUL-3) control katanin levels during this transition, while other complexes like protein phosphatase 4 (PPFR-1) and the Hect E3 ubiquitin ligase (HECD-1/HectD1) control katanin activity through non-degradative means. Interestingly, HECD-1 switches from activating to inhibiting katanin in meiosis and mitosis, respectively. Although mammalian HECTD1 affects protein localization of its targets, mutant worm HECD-1 did not affect localization of known katanin regulators (PPFR-1, MEI-2, MEL-26), suggesting that HECD-1 is acting through novel partners. In mammals, HECD-1 interacts with the striatin-interacting phosphatase (STRIPAK) complex. This complex (without HECD-1) is known to be involved in tubule formation and endocytosis in C. elegans. I found that STRIPAK components genetically interacted with katanin and different components interacted with katanin differently. Generally, the STRIPAK core components (LET-92, GCK-1, CASH-1, FARL-11) acted as katanin activators in meiosis and inhibitors in mitosis, similar to the variable component HECD-1. The core component cerebral cavernous malformations (CCM-3) was an inhibitor of katanin at both divisions. In contrast, variable components (M4.1, OTUB-2) acted as activators of katanin, implying they are inhibitors of the STRIPAK complex. Other components (MOB-4, C49H3.6) were not involved in katanin microtubule-severing. I also used CRISPR flag-tagged HECD-1 and found that HECD-1 is ubiquitously expressed in wild type and
mel-26 mutants (which result in ectopic katanin in mitosis) rather than colocalizing with katanin or microtubules. Additional genetic interactions indicate that the link between STRIPAK and katanin may be through the centralspindlin component ZEN-4 and the tubulin chaperone TBCD-1. My results elucidated the interactions of nearly all of the STIRPAK complex components in a single system and revealed its role in katanin microtubule severing and cell division.